The present invention relates to a scroll type compressor used in an automotive air-conditioner or the like, and more particularly to the shape of scroll body for the purpose of enhancing the performance of the compressor and durability of the scroll body.
As shown in FIG. 6, in general, a conventional scroll body for a scroll type compressor is composed of a stationary scroll body 1 and a movable scroll body 2. Both of the stationary scroll body 1 and the movable scroll body 2 are each composed of a substantially disc-shaped plate member (not shown) and a spiral member 10, 20 formed on one surface of the plate member. The stationary scroll body 1 and the movable scroll body 2 are combined with each other so that their spiral members 10 and 20 are engaged with each other. Then, when the movable scroll body 2 is moved in a circular orbital motion while coming into contact with the stationary scroll body 1 a pair of compression chambers 31 and 32 are formed between the two scroll bodies 1 and 2. Also, the compression chambers 31 and 32 move toward the center of the spiral members 10 and 20. In accordance with this movement, the volume of the compression chambers 31 and 32 is decreased so that any coolant gas therein is compressed.
It is possible to apply a variety of involutes as a curved line for defining the spiral members 10 and 20. However, an involute of a circle that is easy to handle is generally used. However, since a large amount of stress is applied to an initial winding part (i.e., the central end part of the spiral member), in order to increase the mechanical strength of this part, the wall thickness of the spiral members is increased and at the same time, this part is formed into a round shape to avoid sharp edges. For this reason, the point where the involute changes is determined at a suitable involute angular position. The outer end part side of the involute change point is formed into an involute curved line, and the central end part side of the involute change point is formed into another curved line.
Also, the scroll bodies 1 and 2 are generally made of a cast material such as aluminum alloy, and thereafter, finished by machining such as cutting. The inner wall and the outer wall of the spiral members 10 and 20 are conventionally end-milled. In order to further enhance the mechanical strength of the central end part of the conventional scroll bodies 1 and 2 that is subjected to particularly large stress, a cutting tool of an end mill which is different from the tool for the other portions is used for the central end part. As shown in FIG. 8, a radius of curvature R larger than other portions is formed at a root corner end part 5 where the wall surface meets the plate member so as to be more reinforced than other root corner end parts.
For this reason, the machining precision of the wall surface of the central end part is not as good as at the other parts of the scroll bodies. Accordingly, with respect to this central end part, the two spiral members interfere with each other due to machining tolerances, and there is a fear that excessive wear or contact force may occur. Therefore, a relief is formed in order to avoid this interference. For this relief, a cutaway portion 4 is also formed in the inner wall of the central end part as shown in FIG. 7.
FIG. 9 shows a state where the spiral member 20 of the second scroll body (for example, the movable scroll body) 2 is arranged at an interval corresponding to a radius of the revolution relative to the spiral member 10 of the first scroll body (for example, the stationary scroll body) 1.
In FIG. 9, an angular region A1 between a point a1 and a point b1 on the wall surface of the spiral member 10 and an angular region A2 between a point a2 and a point b2 on the wall surface of the spiral member 20 indicate the portions of the spiral members 10 and 20 in which stress is increased. A radius of curvature R larger than that of the other parts is applied to each root corner portion 5 (see FIG. 8) as described above.
In FIG. 9, points a21 and b21 at which normal lines L11 and L12 from the points a1 and b1 of the spiral member 10 intersect with the spiral member 20 are theoretically the points of the associated member with which the points a1 and b1, respectively, come into contact when the scroll bodies 1 and 2 are operated. In the same manner, points a11 and b11 at which normal lines L21 and L22 from the points a2 and b2 of the spiral member 20 intersect with the spiral member 10 are theoretically the points of the associated member with which the points a2 and b2, respectively, come into contact when the scroll bodies 1 and 2 are operated. Thus, in FIG. 9, when a normal line is drawn from any desired point of the inner wall of one of the spiral members, the point on the inner wall of the associated member at which the normal line intersects represents a point at which the two members contact with each other.
However, in the above-described angular regions A1 and A2, since the radius of curvature R larger than that for the other portion is applied to the root corner portion as described above, machining precision is reduced. Accordingly, in region D including the two regions A1 and A2, as indicated by the dotted line in FIG. 9 (or as shown in the perspective view of FIG. 7), the cutaway portion 4 to be used as the relief is provided on the inner wall of the spiral member 20 of the second scroll body 2. Here, in order to facilitate the understanding of the cutaway portion 4 in the drawings of FIG. 7 and FIG. 9, the size thereof is exaggerated.
FIG. 8 is a cross-sectional view of the spiral member 10 of the first scroll body 1 which has been cut away up to the dotted line in FIG. 9. The wall thickness of this part of the spiral member 20 is cut away up to the dotted line so that the wall is thinner than the theoretical shape. The machining tolerance based on reduced machining precision is dealt with by this cutaway portion 4.
In the above-described conventional compressor, the state of contact between the two spiral members 10 and 20 is categorized into three types, i.e., a region in which the portions having the radius of curvature R larger than that of the other portions, as the portion reinforced more than the other root corner portions, namely, the above-described portions in which machining precision are not good, appear in both the spiral members, a region in which the portions appear in one of the spiral members, and a region in which the portions do not appear in any of the spiral members. In FIG. 9, the region B is the region in which the portions that are machined with less precision having the radius of curvature R appear in both the spiral members. In this case, the machining tolerances of both spiral members 10 and 20 are combined to cause such portions with less precision. Also, the regions C1 and C2 are regions in which the portions that are machined with less precision having the radius of curvature R appear in either one of the spiral members 10 and 20. In this case, errors caused by the machining tolerances of one of the spiral members appear. However, the cutaway portion 4 serving as the relief is formed with a constant relief dimension in the region D including these regions B, C1 and C2. For this reason, in the regions C1 and C2 where only one of the machining tolerances appear, the relief action would be excessive, so that the gap between the two spiral members is large. As a result, the performance of the compressor would be degraded. Also, there is a tendency for the durability of the spiral members to become worse due to the extra cutaway portions.